The quality of video that a set-top box outputs may depend on both an encoded video signal that the set-top box receives from a remote video server and capabilities of the set-top box itself.
When the remote video server encodes a movie for transmission, the signal that the video server generates may depend on the precise starting point in the movie, at which the video server begins to encode the movie. Furthermore, due to noise, starting points for different encoding sessions may be different. Consequently, even from the same movie, the video server may be unable to generate an identical video signal.
When set-top boxes of the same make and model receive an encoded video signal from the same video server, the set-top boxes may generate different output video signals. There are many reasons for the differences. One reason may be that the set-top boxes use different decoding algorithms (e.g., different versions of a decoder). Another reason may be that the set-top boxes produce different amounts of noise in the output video signals. Yet another reason may be that, with respect to hue, color, and saturation, each set-top box may be calibrated differently from other set-top boxes. Yet another reason may be that each set-top box is designed to generate output video whose quality depends on a processing load of the set-top box, and the set-top boxes may be under different processing loads. For example, the set-top boxes may use a decoding algorithm in which rendering a particular frame depends on minute delays in processing.